This invention relates generally to web guiding devices and systems and more particularly, it relates to an apparatus for detecting and guiding a web which includes a web scanner bar unit that extends across the entire width of the web path for controlling a steering mechanism to maintain a more precise edge and/or center alignment. In one particular application, the web detecting and guiding apparatus of the present invention is utilized in a high speed continuous web printing press for the purpose of continuously controlling the lateral position of the paper web as it is passed through the press.
During the manufacturing and processing of web-like or sheet-like materials, it is well known in the prior art to employ an edge sensing device which senses the position of one edge of the web or strip and a steering means is actuated when the web deviates more than a predetermined distance from the one edge it is designed to follow. Also, a pair of edge sensing devices located on opposite edges of the web are used when it is desired to guide along an established line taken through the center of the web. Typically, the edge sensing devices consist of a light source and light-responsive detector which must be initially positioned by manual adjustment so as to be in its correct or in register position with the edge of the web. This results in time-consuming labor costs. Further, these edge sensing devices are not well adapted for accommodating webs of varying widths because, in such event, the sensing devices must be again manually re-adjusted either inwardly or outwardly so as to be in register with the side edges of the new web of different width being run.
Moreover, the prior art edge sensing devices are not capable of detecting a break or split in the middle of the web so that a system could be shut down. A break in the middle of the web would not be detected until the break increased to such an extent that it reached the edges. Since a considerable amount of time could pass before such a break was determined, a large waste of material would occur before the system was shut down. In addition, this may cause damage to the system due to snagging or trapping of the web in the guide rollers of the system.
It would therefore be desirable to provide an apparatus for detecting and guiding different width webs on a given edge and/or center line of travel which does not require manual adjustment of the sensing devices when the web width is changed. It would also be expedient to provide an apparatus with the capability of detecting a break in the middle of the web. This is achieved by the web detecting and guiding apparatus of the present invention by the provision of a web scanner bar unit which extends across the entire width of the web path and which has no moving parts. The web scanner bar unit is also utilized to determine a break in the middle of the web.